Washington ? The FBI is warning local police and the U.S. utility, banking and transportation industries of a steady stream of threats mentioning New York, Washington, D.C., and the anniversary of the Sept. 11 attacks.

U.S. military bases and diplomatic missions worldwide are also being placed on high alert for the week, officials say. The U.S. Embassy in Jakarta was closed Monday because of a specific threat against it.

Security is tightening at U.S. military bases and other sites as the one-year anniversary of the 9-11 terrorist attacks approaches. A military helicopter flew Monday over a makeshift memorial at the Shanksville, Pa., site of the crash of United Flight 93. Forty passengers and crew died when the hijacked plane crashed last Sept. 11.

The flurry of incoming threats picked up by intelligence sources is challenging the FBI to determine which might be credible. But while officials say they have no specific details of an impending attack, the government is taking no chances.

White House press secretary Ari Fleischer said Monday the threat of new attacks remained a worry to U.S. officials.

“Anniversaries can be not necessarily always can be occasions for heightened terrorist activity,” Fleischer said. “Just given the fact that it’s a one-year anniversary, we’re going to be on our toes.”

Last week, the FBI posted a bulletin on a Web site and sent a message over a private law enforcement bulletin system advising a state of alert on Sept. 11.

The Web site bulletin was posted by the FBI’s National Infrastructure Protection Center, which assesses threats and passes warnings to local infrastructure companies and agencies. Banks, trucking companies, power companies, utility companies and transportation companies are in the network that the FBI communicates with through Internet bulletins.

Other events mentioned on the Web site as warranting heightened awareness include the Sept. 10-20 U.N. General Assembly session in New York and the Sept. 25-29 World Bank and International Monetary Fund meetings in Washington.

“A large volume of threats of undetermined reliability continues to be received and investigated by the FBI,” the bulletin said. “Several of these threats make reference to the events of Sept. 11, 2001, and to New York City and Washington, D.C.”

The warnings are based on information from all U.S. intelligence sources from telephone calls to interviews with detainees at the U.S. Naval Base in Guantanamo Bay, Cuba, according to a senior law enforcement official.

Information from detainees, most of whom have been out of circulation for months, has proven false before. U.S. officials have said they act on it only when corroborated through multiple sources, but they believe advising caution still is necessary.

A U.S. military helicopter patrols near the Statue of Liberty. Wednesday marks the anniversary of the Sept. 11 attacks, and the military will provide heavy security.

As the Sept. 11 anniversary nears, U.S. intelligence agencies have detected a marked increase in terrorist “chatter” that is, monitored communications and other information used as a barometer of the likelihood of potential attacks.

Recent terror plots in Afghanistan and Germany, however, have not been linked to al-Qaida, said a U.S. counterterrorism official, speaking Monday on condition of anonymity.

In Germany, a Turkish man and his American fiancee, arrested last week on suspicion of plotting to bomb a U.S. military base in Heidelberg, are thought to have been inspired by Osama bin Laden, but U.S. officials doubt the pair is connected to the organization.

If that’s the case, counterterror officials worry that the Turk, Osman Petmezci, and his fiancee, Astrid Eyzaguirre, may represent a new kind of threat wrought by the spectacular nature of the Sept. 11 attacks people who have had no contact with al-Qaida but are moved to action by bin Laden.

U.S. military bases went on alert Monday out of an abundance of caution and not in response to any specific threat, government officials said.

At the State Department, spokesman Richard Boucher said a cable was sent to all diplomatic posts advising them to maintain a higher state of alert Wednesday. A worldwide July 1 caution urging Americans to take extra care remains in effect.

Along with the close of the embassy in Jakarta, the consulate in Surabaya was closed and officials said the U.S. Embassy in Manila was a source of concern.